1. Field of the Invention
This invention relates to digestion with chemical systems which form passivating layers, and more particularly to the removal of passivating layers by a system in which differential duty cycles of particle residence within an ultrasonic field is based upon particle size.
2. Description of the Related Art
For the dissolution and digestion of various silicate and other mineral samples and of glasses for ore processing and for other uses where it is necessary to solubilize the material particles of various sizes, digestion can be expedited if the duty cycle of the particle is a function of the particle size. In other words, larger particles spend more time in the ultrasonic field. If all the material is kept in the ultrasonic digester, the smaller particles which can undergo reasonable passive digestion outside of the apparatus limit the amount of larger particles that can reside in the ultrasonic field. Light particles can be recirculated outside of the circulation vessel with varying duty cycles with reasonable digestion rates. However, large particles which must also be digested should spend more time in the ultrasonic field.
U.S. Pat. No. 5,059,309, issued to C. E. Jordan, discloses an ultrasonic flotation unit which separates material based on their hydrophobic or hydrophilic properties. Particles with no differential properties in this respect will not benefit from this type of flotation. Furthermore, the Jordan system is not applicable to homogenous types of materials which cannot be separated into fractions which float or sink.
U.S. Pat. No. 3,255,999, issued to D. Weston, discloses an apparatus which facilitates reactions with particulate matter. The apparatus is a one pass device with all particles entering an inlet and exiting through an outlet with no effort for internal recirculation or particle segregation. The apparatus injects reagents directly into the mixing zone.
U.S. Pat. No. 4,498,819, issued to A. A. El-Saie, discloses an apparatus for mixing multiple fluid streams for a control output density. It comprises a vessel with a lower conic section and a cylindrical upper section with tangential and axial inlets which provide different fluid streams. Mixing occurs as the fluids flow in a spiral in a direction of decreasing diameter through the cone and out the bottom. The El-Saie device does not segregate particles in accordance with their size.